This invention relates to a high-speed, infinitely adjustable gap cutting sheeter for printed webs or signatures which employs a dual rotary knife system in combination with a synchronized, variable high pressure transient or pulsating air flow in combination with a vacuum chip remover which does not interfere with the continuous flow of the passing sheets or signatures. The rotary knives are two separate assemblies, one synchronized with the other and both synchronized to the passing printed web tracking a pre-printed mark on the printed web. The second knife can be changed in position relative to the first knife so that gap size can be changed instantaneously without any downtime between printing runs having different gap cutting requirements.